PeepholeOpt: Do not skip reg_sequence sources with subregs

[arsenm]

Contrary to the comment, this particular code is not responsible
for handling any composes that may be required, and unhandled cases
are already rejected later. Lift this restriction to permit composes
and reg_sequence subregisters later.

[arsenm]

• PeepholeOpt: Do not skip reg_sequence sources with subregs #125667 👈 (View in Graphite)
• AMDGPU: Use default shouldRewriteCopySrc #125535 : 1 other dependent PR (#125656 )
• PeepholeOpt: Fix looking for def of current copy to coalesce #125533
• X86: Remove hack in shouldRewriteCopySrc for subregister handling #125224
• main

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Author: Matt Arsenault (arsenm)

Changes

Contrary to the comment, this particular code is not responsible
for handling any composes that may be required, and unhandled cases
are already rejected later. Lift this restriction to permit composes
and reg_sequence subregisters later.

---

Full diff: https://github.com/llvm/llvm-project/pull/125667.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/PeepholeOptimizer.cpp (+1-3)
• (modified) llvm/test/CodeGen/AMDGPU/peephole-opt-regseq-removal.mir (+3-3)

diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 745c0d4b36a620..870f3a0fabf24c 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -406,9 +406,7 @@ class RegSequenceRewriter : public Rewriter {
 
     const MachineOperand &MOInsertedReg = CopyLike.getOperand(CurrentSrcIdx);
     Src.Reg = MOInsertedReg.getReg();
-    // If we have to compose sub-register indices, bail out.
-    if ((Src.SubReg = MOInsertedReg.getSubReg()))
-      return false;
+    Src.SubReg = MOInsertedReg.getSubReg();
 
     // We want to track something that is compatible with the related
     // partial definition.
diff --git a/llvm/test/CodeGen/AMDGPU/peephole-opt-regseq-removal.mir b/llvm/test/CodeGen/AMDGPU/peephole-opt-regseq-removal.mir
index e1ff42125ce9a4..333f7de921c247 100644
--- a/llvm/test/CodeGen/AMDGPU/peephole-opt-regseq-removal.mir
+++ b/llvm/test/CodeGen/AMDGPU/peephole-opt-regseq-removal.mir
@@ -22,9 +22,9 @@ body:             |
     ; GCN-NEXT: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
     ; GCN-NEXT: [[COPY1:%[0-9]+]]:vgpr_32 = COPY $vgpr1
     ; GCN-NEXT: [[REG_SEQUENCE:%[0-9]+]]:vreg_64 = REG_SEQUENCE [[COPY]], %subreg.sub0, [[COPY1]], %subreg.sub1
-    ; GCN-NEXT: [[REG_SEQUENCE1:%[0-9]+]]:vreg_64 = REG_SEQUENCE [[REG_SEQUENCE]].sub1, %subreg.sub0, [[REG_SEQUENCE]].sub0, %subreg.sub1
-    ; GCN-NEXT: [[COPY2:%[0-9]+]]:vgpr_32 = COPY [[REG_SEQUENCE]].sub1
-    ; GCN-NEXT: [[COPY3:%[0-9]+]]:vgpr_32 = COPY [[REG_SEQUENCE]].sub0
+    ; GCN-NEXT: [[REG_SEQUENCE1:%[0-9]+]]:vreg_64 = REG_SEQUENCE [[COPY1]], %subreg.sub0, [[COPY]], %subreg.sub1
+    ; GCN-NEXT: [[COPY2:%[0-9]+]]:vgpr_32 = COPY [[COPY1]]
+    ; GCN-NEXT: [[COPY3:%[0-9]+]]:vgpr_32 = COPY [[COPY]]
     ; GCN-NEXT: KILL [[COPY3]], implicit [[COPY2]]
     %0:vgpr_32 = COPY $vgpr0
     %1:vgpr_32 = COPY $vgpr1